Synthesis of indoles and carbazoles from a lignin model compound α-hydroxyacetophenone

Abstract

Most lignin depolymerization products have specific functional groups and possess multiple reactivities, and therefore, have great potential to serve as starting materials for the synthesis of high value-added products. We describe herein an efficient strategy of using an oxidized lignin model compound, α-hydroxyacetophenone, as starting material to synthesize indoles or carbazoles in conjunction with using pyrroles or indoles as counterpart reagents. The reactions were performed using Sc(OTf)₃ as a catalyst in a bio-based green solvent, glycerol, and moderate to excellent yields were obtained. At the end of the reaction, both solvent and catalyst can be recovered and reused. The novel approach presented here not only provides an eco-efficient route for the value-added conversion of lignin degradation products, but also extends the diversity of indole and carbazole derivatives, which are of potential importance in the development of functional photo-electric materials.